Are the world's glaciers threatened by climate change?

A Nature study has shocked researchers by finding that the Himalayas have lost no ice over the past decade. Leo Hickman, with your help, investigates. Get in touch below the line, email your views to leo.hickman@guardian.co.uk or tweet @leohickman

Khumbu glacier in the Everest-Khumbu region, one of the longest glaciers in the world. Photograph: Subel Bhandari/AFP/Getty Images

10.27am: Researchers are said to be shocked by a new study published in Nature that has found the world's largest mountain chain, which stretches from the Himalayas to Tian Shan on the border of China and Kyrgyzstan, has lost no ice over the past decade.

Scientists had previously claimed that climate change is causing a net loss of ice and water from the glaciers and ice caps that straddle the Himalayas and other mountain ranges around the world. As Damian Carrington's report of the study says:

The study is the first to survey all the world's icecaps and glaciers and was made possible by the use of satellite data. Overall, the contribution of melting ice outside the two largest caps – Greenland and Antarctica – is much less then previously estimated, with the lack of ice loss in the Himalayas and the other high peaks of Asia responsible for most of the discrepancy.

So, does this place a large question mark over the common assertion that climate change is causing the world's glaciers to melt? Photographs showing how much glaciers have retreated over the past century or so have become a totemic symbol of climate change. Glaciers are often described as climate change's "canary in the mine".

But, as Carrington highlights, claims about Himalayan glaciers melting have proved controversial with the UN's Intergovernmental Panel on Climate Change admitting in 2010 that it had mistakenly stated in one of its landmark reports that they would disappear by 2035, instead of 2350.

The Nature paper comes with some big caveats and disclaimers, though:

"Our results and those of everyone else show we are losing a huge amount of water into the oceans every year," said Prof John Wahr of the University of Colorado [who led the study]. "People should be just as worried about the melting of the world's ice as they were before."His team's study concludes that between 443-629bn tonnes of meltwater overall are added to the world's oceans each year. This is raising sea level by about 1.5mm a year, the team reports, in addition to the 2mm a year caused by expansion of the warming ocean.The scientists are careful to point out that lower-altitude glaciers in the Asian mountain ranges – sometimes dubbed the "third pole" – are definitely melting. Satellite images and reports confirm this. But over the study period from 2003-10 enough ice was added to the peaks to compensate...Wahr warned that while crucial to a better understanding of ice melting, the eight years of data is a relatively short time period and that variable monsoons mean year-to-year changes in ice mass of hundreds of billions of tonnes. "It is awfully dangerous to take an eight-year record and predict even the next eight years, let alone the next century," he said.

But what are your own thoughts and conclusions about the impact of climate change on glaciers? Should we be concerned if glaciers are melting?

If quoting figures to support your points, please provide a link to the source. I am particularly seeking links to data and papers which show the wider, global picture regarding the impact of climate change on glaciers, and, crucially, the impact on humans and habitats if they do melt. I will also be inviting various interested parties to join the debate, too. And later on today, I will return with my own verdict.

There are more than 160,000 glaciers and ice caps worldwide. Fewer than 120 (0.075%) have had their mass balance (the sum of the annual mass gains and losses of the glacier or ice cap) directly measured, and for only 37 of these are there records extending beyond 30 years. Extrapolating this tiny sample of observations to all glaciers and ice caps is a challenging task that inevitably leads to large uncertainties.[The new] study based on satellite data for Earth's changing gravity field tackles this problem. Their results have surprising implications for both the global contribution of glaciers to sea level and the changes occurring in the mountain regions of Asia...First, the contribution of glaciers and ice caps (GICs) (excluding the Antarctica and Greenland peripheral GICs) to sea-level rise was less than half the value of the most recent, comprehensive estimate obtained from extrapolation of in situ measurements for 2001–05 (0.41 ± 0.08 compared with 1.1 mm yr−1). Second, losses for the High Mountain Asia region — comprising the Himalayas, Karakoram, Tianshan, Pamirs and Tibet — were insignificant. Here, the mass-loss rate was just 4 ± 20 gigatonnes per year (corresponding to 0.01 mm yr−1 of sea-level rise), compared with previous estimates that were well over ten times larger. By a careful analysis, the authors discounted a possible tectonic origin for the huge discrepancy, and it seems that this region is more stable than previously believed.What is the significance of these results? Understanding, and closing, the sea-level budget (the relative contributions of mass and thermal expansion to ocean-volume change) is crucial for testing predictions of future sea-level rise. Estimates of the future response of GICs to climate change are, ingeneral, based on what we know about how they have responded in the past. A better estimate of past behaviour, such as that obtained by Jacob and colleagues, will therefore result in better estimates of future behaviour.Discussion of the demise of the Himalayan glaciers has been mired in controversy, partly because of basic errors, but also because of the dearth of reliable data on past trends. Given their role as a water supply for so many people, this has been a cause for concern and an outstanding issue...Jacob and colleagues have dramatically altered our understanding of recent global GIC volume changes and their contribution to sea-level rise. Now we need to work out what this means for estimating their future response.

These reports provide a new baseline and location-specific information for understanding climate change in one of the most vulnerable ecosytems in the world.

The first report focused on the stability of the region's glaciers:

The HKH region, home to 30 percent of the world's glaciers, has been called the "Third Pole." But there are scant data on these glaciers. One of the reports, The Status of Glaciers in the Hindu Kush-Himalayan Region—presenting findings of a three-year Sweden-funded research project led by ICIMOD—begins to fill in the important data gaps. Using remote sensing studies, the project was able to tally the number of glaciers in the region—more than 54,000—and measure the area covered, 60,000 km.Of these 54,000 glaciers, however, only ten have been studied regularly to determine the net loss or gain of ice and snow (called the mass balance). That handful of studies shows a loss of mass balance, with the rate of loss roughly doubling between 1980 and 2000 and 1996 and 2005. In the Everest area, the data show a marked acceleration in the loss of glacial mass between 2002 and 2005. Glaciers appear to be shrinking in both the central and eastern Himalayas. Country-specific studies have found that depletion of glacial area over the past 30 years was 22 percent in Bhutan and 21 percent in Nepal. The clean glaciers of the Tibetan plateau are retreating at a faster rate than the glaciers of the rugged central Himalayas, which have higher debris cover; debris creates an insulating effect, slowing melting.

The third report dealt with likely impacts if the region's glaciers melt:

Increases in glacial melting are projected to limit the natural water storage provided by expanses of snow and ice and to heighten the risk of glacial lake outburst floods. Mass losses from glaciers and accelerating reductions in snow cover are expected to ultimately reduce water supplies and hydropower potential. Changes in the seasonality of flows in river basins supplied by melt water from snow and ice are also predicted. Droughts will likely affect greater areas, and with dry spells there will need to be greater reliance on irrigation, even as water sources become more restricted, according to the authors. The risk of flooding is also increasing with increased variability of climate.

A growing number of studies based on satellite data and stream chemistry analyses have found that far less surface water comes from glacier melt than previously assumed. In Peru's Rio Santa, which drains the Cordilleras Blanca mountain range, glacier contribution appears to be between 10 and 20 percent. In the eastern Himalayas, it is less than 5 percent...The Himalayan glaciers feed into Asia's biggest rivers: the Indus, the Ganges and the Brahmaputra in India, Pakistan and Bangladesh, and the Yellow and Yangtze rivers in China. Early studies pegged the amount of meltwater in these river basins as high as 60 or 70 percent. But reliable data on how much water the glaciers release or where that water goes have been difficult to develop. Satellite images can't provide such regular hydrometeorological observations, and expeditions take significant time, money and physical exertion.New methods, though, are refining the ability to study this and other remote glacial mountain ranges. Increasingly, scientists are finding that the numbers vary depending on the river, and even in different parts of the same river."There has been a lot of misinformation and confusion about it," said Peter Gleick, co-director of the California-based Pacific Institute for Studies in Development, Environment and Security. "About 1.3 billion people live in the watersheds that get some glacier runoff, but not all of those people depend only on the water from those watersheds, and not all the water in those watersheds comes from glaciers. Most of it comes from rainwater," he said.

12.43pm: Here is the all-important table of data from the Nature paper. It is headed, "Inverted 2003-2010 mass balance rates", and shows the world's 20 largest GICs (glacier and ice cap regions) and by how many gigatonnes (Gt) each one has increased or decrease over that time period. Crucially, it also shows the margin of error. You will see that some regions record little change or near parity between these figures, most notably - hence the headline finding from the study - the regions of the Himalayas and its surrounds (numbered 8, 8a, 8b, 8c, and 8d).

Glaciers

Ignore

Region

Rate (Gt yr-1)

1

Iceland

-11.±.2

2

Svalbard

-3.±.2

3

Franz Josef Land

0.±.2

4

Novaya Zemlya

-4.±.2

5

Severnaya Zemlya

-1.±.2

6

Siberia and Kamchatka

2.±.10

7

Altai

3.±.6

8

High Mountain Asia

-4.±.20

8a

Tianshan

-5.±.6

8b

Pamirs and Kunlun Shan

-1.±.5

8c

Himalaya and Karakoram

-5.±.6

8d

Tibet and Qilian Shan

7.±.7

9

Caucasus

1.±.3

10

Alps

-2.±.3

11

Scandinavia

3.±.5

12

Alaska

-46.±.7

13

Northwest America excl. Alaska

5.±.8

14

Baffin Island

-33.±.5

15

Ellesmere, Axel Heiberg and Devon Islands

-34.±.6

16

South America excl. Patagonia

-6.±.12

17

Patagonia

-23.±.9

18

New Zealand

2.±.3

19

Greenland ice sheet.+.PGICs

-222.±.9

20

Antarctica ice sheet.+.PGICs

-165.±.72

Total

-536.±.93

GICs excl. Greenland and Antarctica PGICs

-148.±.30

Antarctica.+.Greenland ice sheet and PGICs

-384.±.71

Total contribution to SLR

-1.48.±.0.26

SLR due to GICs excl. Greenland and Antarctica PGICs

-0.41.±.0.08

SLR due to Antarctica.+.Greenland ice sheet and PGICs

-1.06.±.0.19

But look, too, at the significant net loss of ice mass in regions such as Alaska, Greenland and Antarctica. The overall picture is that, yes, there are regional variabilities, uncertainties and stability, but that there was a net loss of ice mass globally - 536Gt (+/- 93Gt) - between 2003 and 2010.

The overall picture from this study is that, on the whole, the global volume of glacier ice is reducing, with important implications for sea level rise. Importantly, however, it also demonstrates the complexity of glacier response to what seems to be a progressively warming climate.All too often in the past media reports have presented a "black and white" view of climate change and glacier response to climate change. This may appeal to some, depending on their respective agendas, but scientists have long recognised the complexity of the situation.For example, the Arctic region is experiencing a much greater rate of warming than other areas of the Earth. This appears to correlate with the glacier losses (e.g. Ellesmere, Baffin Island, Greenland) presented by Jacob et al. Elsewhere, the picture is different. Perhaps one of the more intriguing findings of this study is that there is relatively little change in the high Asian mountains (e.g. Himalaya, Karakoram).Some will remember from back in late 2009 the Indian Ministry of Environment and Forests report by VK Raina suggested a similar finding. This prompted a follow-up article in Science by Pallava Bagla and an article, also in Science, by scientists Cogley et al (pdf) who traced the source of an important error that had been propagated in earlier literature that Himalayan glaciers were set to disappear by 2035 (it turns out this should have been 2350).The reasons for this complex global picture are not clear: some places warm more than others, some places experience more precipitation and, hence, snowfall to maintain glaciers is in positive or neutral balance. What is clear is that more research is required to evaluate the response of glaciers to climate change.

2.15pm: And here's an assessment of the Nature paper by Dr Richard Hodgkins, senior lecturer in physical geography at Loughborough University:

(1) Mass-loss estimates from the Himalayan region have been revised downward on the basis of a refined technique, but mass is still being lost;(2) This is a welcome contribution for a part of the world which is incredibly hard to monitor on the ground (hence the uncertainty of previous estimates), and even from space;(3) They key human angle is what this means for the water yield from river basins to which Himalayan glaciers contribute: glacier stability or growth at the highest elevations may have little impact on water yields, whereas ongoing loss at lower elevations may be much more detrimental. This question is really hard to resolve, however;(4) There's no room for complacency: even very small changes in water supplies have the potential to impact tens or hundreds of millions of people, given how populous Asia is downstream of the Himalayas (but if jeopardy is potentially reduced, hooray);(5) The remainder of the Nature paper documents ongoing ice loss from all parts of the world, including Greenland and Antarctica.

1) Is it reasonable to assume that the general tendency is that, globally, glaciers are retreating?

Yes. If you look at the larger glaciers systems (Alaska, Canadian Arctic, Patagonia, Antarctica, Greenland) they all show a significant -ve trend that is larger than the uncertainty. For the smaller systems, such as the Alps, where there is relatively good in-situ observations, these also show a -ve trend. The uncertainties in the GRACE estimates for these smaller systems are about the same size as the signal, which is why hard to use them to determine smaller loss terms.

2) For people studying climate change, what is the most meaningful timescale? Does it make most sense to look at changes (in whatever indicators are being measured) on a year-by-year basis, a decade by decade basis, a century by century basis- or some other timescale?

This all depends on the system you're interested in and what you want to know. For example, the deep, abyssal circulation in the ocean takes thousands of years, while mesoscale eddies at the surface come and go over a few weeks. Generally, 30 years is considered to be a reasonable period for looking at climatological means that are controlled be atmospheric processes. In other words, over this timescale, inter-annual variability is reduced so that trends should be visible. In my article, and in the authors paper, we acknowledge that 8 years is a short time period and it is important, therefore, not to over-interpret the results.

2.37pm: I have just received this response from Graham Cogley, professor of geography at Trent University in Ontario, Canada:

"My general take is that Jacob et al. (of which I already have a copy) is a welcome look at global glacier mass balance from a fresh perspective. It is consistent with some other lines of evidence that suggest that the earlier estimates may have overestimated the rate of loss. On the other hand it still needs work; GRACE cannot really "see" a good many of the regions with lesser amounts of glacier ice (the ones where the rate is not significantly different from zero in their Table 1), so for example it would be nice to know whether those lesser regions would make much of a difference. (With rare exceptions it is not plausible that any of them are actually gaining mass in the form of glacier ice.)"

I should explain that GRACE cannot "see" smallish collections of glaciers, such as those in the European Alps, because it has low spatial resolution. But the traditional methods make it quite clear that, whenever they are measured, the smallish collections are indeed losing mass. They count for little in the big picture because they account for only a small proportion of the total extent of ice.One of the most convincing things in the paper by Jacob and others is the demonstration that earlier estimates of rapid mass loss in the eastern Himalaya are implausible. Further west, in the Karakoram, the GRACE finding of stability or even mass gain is consistent with other lines of evidence, including some that are not yet in the peer-reviewed literature. (So the Karakoram is the main "rare exception" at the moment.Two final points:Technically, GRACE is potentially a great leap forward because it measures mass change *directly*. But it is going to fall out of the sky in the next couple of years, and the follow-on to GRACE will not fly until several years from now. So we will have to rely on the traditional methods for at least a while longer, and part of the technical challenge is to learn how to use what GRACE is telling us to improve how we make regional estimates from the traditional sparse, scattered measurements.Second, one of the points made correctly by Jacob and others is that the traditional measurements show a slowdown in the rate of loss since about 2005. So far the reasons for this have not been investigated, and it is a very intriguing phenomenon - because the temperature records, for example, do not seem to show the same pattern of change. But to the extent that the glaciers had several "bad" years in the early 2000s, and published estimates based on the traditional measurements are still weighted more towards those years than the most recent years, the disagreement may not be as "dramatic" as some statements in the media might suggest. (We still can't explain the slowdown, though.)

My verdict

The Nature study has inevitably attracted plenty of attention because it deals, in part, with the still-controversial subject of Himalayan glaciers. Climate sceptics were delighted in 2010 when the IPCC had to correct a silly mistake in one of its landmark reports in which it had used "grey literature" to mistakenly make the claim that the region's glaciers would melt by 2035, rather than 2350, if current warming trends continued.

The surprising finding, reported in this new study, that satellite evidence shows that there wasn't any loss in ice mass between 2003 and 2010 in the wider Himalayan region has, again, been welcomed with much delight by climate sceptics. However, the headline finding distracts somewhat from the rest of the data presented in the paper. It shows clear evidence that other regions, most notably Greenland and Antarctica, recorded a significant loss in ice mass over this same period. But, because this was largely expected, it didn't become the headline.

There's little comfort to be found, though, in the news that, in total, 536 gigatonnes (+/- 93Gt) of ice was "lost" globally between 2003 and 2010. What this study shows is that our understanding of how glaciers are affected by climate change can, as you would expect, be improved. For example, there are huge regional variations for reasons that scientists are still trying to fully understand. But to pin our hopes that climate change might be more benign than first feared on an unexpected finding in one region over a period of just eight years seems unwise when the wider global trend is clear, as the study clearly shows.

About this article

Are the world's glaciers threatened by climate change? | Leo Hickman

This article was published on
the Guardian website
at 10.13 EST on Thursday 9 February 2012.
It was last modified at 21.10 EDT on Tuesday 3 June 2014.
It was first published at 05.28 EST on Thursday 9 February 2012.